A spray‐dried dual microbial Wettable powder formulation: optimization and greenhouse efficacy against Western flower Thrips

Abstract

Abstract BACKGROUND This study aimed to develop and evaluate a spray‐dried wettable powder (WP) formulation containing the entomopathogenic bacterium Serratia marcescens and the fungus Metarhizium flavoviride for the control of Frankliniella occidentalis . RESULTS The formulation was optimized using a Taguchi experimental design to maximize viable microorganism counts while maintaining suitable physicochemical properties. The optimal formulation achieved a high microbial load (3.18E+12 CFU/g) with favorable characteristics, including good suspensibility (79.4%), a low wetting time (27.4 s), an appropriate particle size (11.54 μm), and an acceptable moisture content (7.43%). The formulation also demonstrated strong thermal stability under different storage conditions. Laboratory bioassays revealed a clear dose‐dependent increase in mortality in both larval and adult stages, with significant differences among treatment concentrations. The highest dose (100 g/100 L) consistently produced the greatest mortality. Greenhouse trials conducted in two different locations confirmed the efficacy of the formulation under practical conditions, achieving up to 92.6% control and showing performance comparable to that of a commercial product. CONCLUSION These findings indicate that the combined use of bacterial and fungal agents in an optimized WP formulation provides an effective and sustainable alternative for the management of F. occidentalis . © 2026 Society of Chemical Industry.